The present invention relates to liquid ejection apparatuses ejecting liquid from liquid ejection heads as liquid droplets, such as inkjet recording apparatuses, display manufacturing apparatuses, electrode manufacturing apparatuses, and biochip manufacturing apparatuses, as well as liquid filling methods of the liquid ejection apparatuses.
Conventionally, inkjet printers are known as the liquid ejection apparatuses, which eject liquid from nozzles of an ejection head as liquid droplets. Some of the inkjet printers employ off-carriage type ink supply systems. More specifically, in these systems, liquid containers are installed outside carriages.
For example, Japanese Laid-Open Patent Publication No. 2003-211689 describes a printer that has a large-capacity ink cartridge located as spaced from an ejection head and supplies ink from the ink cartridge to the ejection head through a supply tube. The printer further includes a sub tank formed by a flexible container that is arranged between the ink cartridge and the ejection head. An open-close valve is deployed between the ink cartridge and the sub tank for selectively opening and closing the supply tube.
The publication also describes an initial ink filling method of the printer. The method is performed before initial use of the printer for filling a passage including the supply tube and the sub tank (hereinafter, referred to as a “supply passage”) with the ink from the ink cartridge. This is typically performed by sealing a nozzle surface of the ejection head using a cap and depressurizing the interior of the cap, thus drawing ink from communication lines through the nozzles.
At this stage, it is necessary to draw the ink from the supply passage without generating bubbles in the passage. However, if the printer is an off-carriage type including an extremely long passage as in the case of Japanese Laid-Open Patent Publication No. 2003-211689, the speed at which the ink flows through the supply passage cannot be increased sufficiently for suppressing bubble generation, due to anti-movement resistance of the ink, or head loss. Particularly, if the supply passage includes an enlarged portion such as the sub tank, an air layer is easily formed in this portion. This is a major factor that hampers the ink fill.
So as to solve this problem, the initial ink filling method of the aforementioned document involves choke suction. That is, suction is performed with the open-close valve held in a closed state, or in a choked state. This causes relatively great negative pressure in a portion downstream from the open-close valve. The negative pressure acts to remove the air from the sub tank. If the open-close valve is opened in this state, the ink is efficiently supplied to the supply passage.
Nonetheless, even by the choke suction, the ink cannot be supplied entirely to the supply passage without generating the bubbles by a single cycle of operation. Therefore, multiple cycles of ink suction must be performed after the choke suction. In this manner, or by filling the supply passage with the ink through the multiple cycles of ink suction, pulsation is generated in the ink flow in such a manner as to efficiently discharge the bubbles.
However, in this case, a relatively large amount of ink is wasted, particularly if the printer has the off-carriage type ink supply system. This is disadvantageous economically and environmentally.